Apoptosis inhibitors and regenerative nanomedicines
Senescence can be considered a stress response intensified by genomic damages, nucleotide mutations, telomere attrition, protein aggregation or misfolding, and oxidative damage causing or initiating the age-related diseases. Moreover, senescent cells can participate in the induction of pro-inflammatory phenotype (Campisi, 2013; Childs, Durik, Baker, & Van Deursen, 2015; McHugh & Gil, 2018; Muñoz-Espín et al., 2013; Serrano, 2014). The production of pro-inflammatory agents and suppression of cell proliferation are two important hallmarks of senescence response that alter the intracellular and intercellular communications (Childs et al., 2015). The findings have shown a complex correlation between senescent cells, apoptosis, and mitochondrial malfunction with increased age (Sun et al., 2016). Studies on mice and human models have confirmed the accumulation of the senescence biomarkers in tissues, which are associated particularly with atherosclerosis, cancer, rheumatoid arthritis  (RA), and neurodegenerative disorders (Campisi, Andersen, Kapahi, & Melov, 2011; Erusalimsky & Kurz, 2005; Krizhanovsky et al., 2008).
Nanomaterials can be functionalized with ligands, immunoglobulins, or polymers for selective targeting of senescent cells which can be used for therapeutic purposes in addition to diagnostic applications. Besides, the capability of the nanomaterials in detection of cancer cells or induction of apoptosis, some nanomaterials are known in regenerative medicine. Moreover, they can have a determinant role in the restoration of aged, disturbed, damaged, or even lost cells resembling their original structure and function. Additionally, these materials can have the extra potential to diminish the disadvantageous phenotype of the aged cell by modulating the senescence-associated secretory phenotype (SASP) (Salminen, Kauppinen, & Kaarniranta). They can maintain tissue-associated functions with encapsulated inhibitors, small molecules, and effectors, or by reprogramming these cells (Muñoz-Espín, 2019). The progress in nanotechnologies and nanomedicines to treat the senescent cells as anti-aging agents is however still in its infancy, and since the toxicity of many of them has been proven, the important limitation in their application is accompanied by the concern of their safety for human and environment. Some of the nano-compounds that are shown effectivity in inhibiting apoptosis or cells regenerating are listed in Table 5 .